The avalanche danger is HIGH this morning in the backcountry around June Mountain, the Mammoth Lakes Basin and Rock Creek.
Over the past 24 hours, close to 2 feet of snow and 2 inches of water has fallen at the 9,000 ft elevations on June Mountain, Mammoth Mountain and in Rock Creek. More snow has fallen above 9,500 ft and strong southerly and southwesterly winds have transported more snow onto exposed leeward east through north facing slopes. I expect natural avalanches have occurred and continue to occur in steep, upper elevation terrain where loading rates were the highest. Human triggered avalanches are very likely today.
Today, very dangerous avalanche conditions exist on windloaded slopes steeper than 30 degrees. On non-wind affected slopes, which are few and far between, natural avalanches are possible and human triggered slides are likely.
This danger rating does not include ski areas or highways were avlanche control is done.
Likelihood ?CertainVery LikelyLikelyPossible
Size ?HistoricVery LargeLarge
Storm slabs and wind slabs are the main avalanche problem. Temperature swings during the most intense part of the storm of up to 4 degrees F in one hour created distinct layers in the storm snow that fell yesterday. I found a thin layer of graupel about 7 inches down from the snow surface in the Rock Creek area yesterday. A similar 4 degree change if air temperature was recorded yesterday morning after about 6-8 inches of snow had accumulated on Mammoth Mountain and on the Mammoth Pass snow pillow.
While the wind directions recorded at the top of Mammoth Mountain showed sustained strong southwesterly winds, the steep slopes below the summit showed variable wind directions from the south, southeast and southwest wind directions. Expect fresh wind slabs on all north and east facing slopes- layers of wind slabs formed over the last two days offer widespread opportunities to trigger a large slab avalanche. The best way to avoid trouble today is to enjoy the lift skiing on Mammoth and June Mountain or touring in low angle terrain.
Mid elevation slopes including open glades and steep trees exposed to cross loading such as in the Sherwins are likely to produce natural and human triggered avalanches today. People without excellent avalanche skills should avoid these areas today.
The persistent depth hoar and facet layer in the Mammoth Lakes Basin is buried under a lot of snow after yesterday’s storm. The snowpack received a heavy load of 2-3 inches of water in a short period of time. Will the new load activate the dormant facet layer? Do not rule out the possibility.
In the Rock Creek area, the total snowpack depth is a little over 2 feet compared to 6 feet in the Mammoth Basin. Half of the snowpack in Rock Creek from the ground up is well developed depth hoar that has been recently reactive in propagation tests. The persistent weak layer is as much of an avalanche concern as is the wind loading from this storm in Rock Creek. Skiing opportunities are limited to touring to the roads and campgrounds but be aware of the many steep avalanche paths above the roads. Natural avalanches are likely today in the Mammoth, June and Rock Creek areas.
Yesterday, very heavy snowfall rates observed with unusually high loading occurred. Temperatures varied by several degrees. Test slopes were very sensitive to the weight of a skier. A series of extended column tests failed either on isolation or within 10 taps. High loading rates, strong winds and easy failures in tests all indicate very dangerous avalanche conditions.
|0600 temperature:||20 deg. F.|
|Max. temperature in the last 24 hours:||28 deg. F.|
|Average wind direction during the last 24 hours:||SW|
|Average wind speed during the last 24 hours:||50 mph|
|Maximum wind gust in the last 24 hours:||70 mph|
|New snowfall in the last 24 hours:||24 inches|
|Total snow depth:||65 inches|
Ridgetop winds are blowing steady out of the west southwest this morning at 40 mph at the top of Mammoth Mountain. Winds are out of the south at the top of June Mountain. Snow showers continue today but little accumulation is expected. High temperatures reach the low 30’s today at all elevations.
Next week is expected to bring more precipitation as additional storms move into the west coast.